The Section has continued its studies aimed at elucidating the molecular mechanisms of heritable disorders of connective tissue, specifically osteogenesis imperfecta (OI) and Ehlers-Danlos (EDS), and at applying this information to the treatment of these disorders. One continuing interest of the Section is to identify the collagen mutations in patients with OI and EDS and determine the relationship between the type and location of the mutation and the severity of the connective tissue disorder. Mutations in the alpha2(I) collagen chain identified by this Section and other labs have provided additional support for the regional model we have proposed. There are three primary projects in the Section. One primary project is to develop selective antisense suppression of the mutant collagen allele as an approach for therapeutic intervention. This year we have turned to the use of antisense hammerhead ribozymes. In vitro, we have demonstrated allele- specific cleavage and determined the parameters for cleavage. We have conducted competition experiments with total RNA and synthetic targets. We are now pursuing vector constructs to determine suppression stability and efficiency in cultured cells. The second primary project is the generation of a murine model for non-lethal OI. We have used site-directed mutagenesis to produce a construct with a point mutation mimicking non-lethal human OI. The cre-lox recombination system will be used to control the timing of expression of the mutation and a lox-stop-lox construct has been introduced into the intron prior to the exon containing the disease-causing mutation. We have isolated recombinant ES cells and have successfully generated chimeras. A third major focus of interest which we have been developing is in the bone biology of OI. We are using cultured osteoblasts to study the way bone cells modify and secrete mutant collagen. We are also pursing the secondary non-collagenous abnormalities of OI matrix and the response of OI osteoblasts to TGF-beta stimulation. In clinical studies, we are continuing our treatment trial of growth hormone in short children with OI to determine its effects on growth stimulation, bone density and bone morphometric properties. We are continuing our collaborative interests in the neurological aspects of OI and in maximizing the physical functioning of OI children though aggressive rehabilitation.